Lease Commitments - Components of Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 30,418	$ 31,963
Amounts capitalized	(3,395)	(3,913)
Total operating lease expense	27,023	28,050
Financing lease cost:
Amortization of right-of-use assets	3,412	973
Interest on lease liabilities	511	194
Amounts capitalized	(2,810)	(704)
Total financing lease expense	1,113	463
Variable lease expense	221	96
Short-term lease expense	295	414
Total lease expense for the period	28,652	29,023
Public Service Company of New Mexico
Lessee, Lease, Description [Line Items]
Operating lease cost	27,302	28,254
Amounts capitalized	(1,020)	(1,319)
Total operating lease expense	26,282	26,935
Financing lease cost:
Amortization of right-of-use assets	1,563	481
Interest on lease liabilities	221	92
Amounts capitalized	(1,056)	(280)
Total financing lease expense	728	293
Variable lease expense	221	96
Short-term lease expense	288	346
Total lease expense for the period	27,519	27,670
Texas-New Mexico Power Company
Lessee, Lease, Description [Line Items]
Operating lease cost	2,870	3,341
Amounts capitalized	(2,375)	(2,594)
Total operating lease expense	495	747
Financing lease cost:
Amortization of right-of-use assets	1,775	466
Interest on lease liabilities	285	100
Amounts capitalized	(1,754)	(423)
Total financing lease expense	306	143
Variable lease expense	0	0
Short-term lease expense	5	26
Total lease expense for the period	$ 806	$ 916